The major histocompatibility complex class II antigens have as one of their primary functions the presentation of antigen to T helper cells. The expression of these proteins in the proper cells, and at the proper time, is critical for the effective functioning of the immune system. Our primary interest is to examine how the genes coding for the MHC class II antigens are regulated in both a cell specific manner and by cytokines. Central to the regulation of these genes is the assembly of transcription factors on the cis-acting elements located upstream of the genes. In order to better understand how these factors work, we propose to identify and characterize the transcription factors involved in MHC class II gene expression. The initial goal will be to identify DNA binding proteins that bind to the upstream region of the MHC class II gene, I-Abeta. Because of the low quantities of these proteins in cells, we have designed several approaches to clone the genes for these DNA binding factors. Once the genes have been cloned, we will be able to generate sufficient quantities of protein for a more detailed characterization of the proteins. Basically, we would like to know if these DNA binding proteins reflect the transcriptional activity of the I-Abeta gene. Possible changes to be investigated include the splicing pattern of the genes and the phosphorylation status of the proteins. Any change found will be tested for its influence on transcription. It is likely that there are proteins that associate with the DNA binding proteins via protein-protein interactions. A second goal of ours will be to identify these types of proteins. The presence or absence of a particular protein in cells that express MHC class II genes may provide new ideas on how the class II genes are regulated. If we see a protein expressed only in cells that express class II genes, this protein will be an excellent candidate for further characterization. We also propose to study the expression of MHC class II genes in patients with a deficiency in MHC class II expression. It is possible that the deficiency has its basis in a transcription factor. We will begin this study by examining the genes for the DNA binding proteins we have characterized for any defects. A mutation in the activation domain of one of these proteins may be sufficient to alter drastically the expression of the class II gene. Finally, we will test various I-Abeta constructs in transgenic mice. The design of these experiments is to identify new cis-acting elements that may be important for the developmentally regulated expression of the I-Abeta gene.